As for the builder wanting to give you $10K off the price if you don't have any agent, ask yourself this...why?
Without an agent, you have no one representing you or looking out for your best interests. You not having someone in your corner who knows the ins and outs of real estate and new construction is easily worth $10K to a builder who may or may not be above board or doing the right thing.
The builder bribing you to not have an agent is like the person suing you for $300K offering to sue you for only $290K if you don't have a lawyer present.
Most Buyer Agency Agreements will include any property which you enter into contract to purchase during the term of the agreement, whether or not the agent was the procuring cause. Even after the expiration or termination of the agreement, the broker may still be due a commission on any property the agent may have shown or described to you, until a predetermined period of time has elapsed. Many of these agreements conveniently do not include a early termination provision.
If you want to terminate the agreement, and protect yourself from any breach of contract, I would suggest sending a firm and clear letter stating that you desire to terminate the Agreement with the broker. Within the letter, request that the broker provide you a written confirmation of the termination and a complete list of all properties the agent introduced you to during the term of the Agreement.
Once you receive these documents, you may be able to go forward with purchasing any property not on the broker's listing without any commission being owed. Please be advised that this advice is based on Agreements which I have personally reviewed. Without seeing your actual Agreement, I would still recommend that you read it very carefully and/or consult with an attorney before relying on my advice.
If you want tp change agents shop around and hire another agent to represent you in you new home purchase, be it the new construction you mention or another resale house. It is best to be represented by an agnet that will work for your best interests.
Stan Reed, Realtor
Essential elements to both would include an expiration, description of property sought, retainer fee (usually $0), compensation amount (usually seller pays all commission), a broker's fee, termination agreement (days to cancel agreement), protection period (say I would show you two dozen homes over the course of a month and the next weekend you walk into an open house without me and buy it, this would be covered by my protection period in a binding agreement). A non-binding simply states the agent is representing you for that particular property you are writing on at that moment, no other obligations.